Decreased expression of hyperpolarisation-activated cyclic nucleotide-gated channel 3 in Hirschsprung's disease

AIM: To determine if hyperpolarisation-activated nucleotide-gated(HCN) channels exist in human colon, and to investigate the expression of HCN channels in Hirschsprung's disease.METHODS:We investigated HCN1,HCN2,HCN3 and HCN4 protein expression in pull-through specimens from patients with Hirschsprung’s disease(HSCR,n=10)using the proximal-most ganglionic segment and distalmost aganglionic segment,as well as in healthy control specimens obtained at the time of sigmoid colostomy closure in children who had undergone anorectoplasty for imperforate anus(n=10).Fluorescent immunohistochemistry was performed to assess protein distribution,which was then visualized using confocal microscopy.RESULTS:No HCN1 channel expression was observed in any of the tissues studied.Both HCN2 and HCN4proteins were found to be equally expressed in the aganglionic and ganglionic bowel in HSCR and controls.HCN3 channel expression was found to be markedly decreased in the aganglionic colon vs ganglionic colon and controls.HCN2-4 channels were seen to be expressed within neurons of the myenteric and submucosal plexus of the ganglionic bowel and normal controls,and also co-localised to interstitial cells of Cajal in all tissues studied.CONCLUSION:We demonstrate HCN channel expression in human colon for the first time.Reduced HCN3expression in aganglionic bowel suggests its potential role in HSCR pathophysiology.